Exercise and Resistance to Infection Sedentary individuals are prone to infection Moderate exercise attenuates susceptibility to infection Excessive exercise may increase risk of infection above both moderate and sedentary rates

J-shaped Model of Resistance to Infection

Why? Moderate exercise –improves circulation –promotes protein synthesis –stimulates blood cell production

Evidence for Moderate Exercise 45 min, 5 times/week of brisk walking had 1/2 as many days with URTI compared to sedentary group elderly who walked 40 min, 5 times /week had less than 1/2 the incidence of URTI compared to sedentary (21% vs. 50%)

Excessive exercise stimulates cortisol –promotes protein breakdown –inhibits anabolism –inhibits immunological function

Evidence for Excessive Exercise 6 times as many runners got URTI compared to non-participating runners runners training 96 km/week had 2 x URTI as those doing 32 km/week races of km do not increase the risk of URTI in the week following competition

Link Between Muscle and Systemic Physiology (or Why is Specificity Important?) Training study –trained one leg for 13 sessions –(15 which elicited HR = 170) –at the beginning of the study & end of each week, NE,E, LA, V E were tested at same initial workload –training effect was observed all variables were lower at submaximal workload

Was the Training Effect Systemic or Muscular after 13 sessions the untrained leg was trained for 5 sessions at same workload as trained leg if training effect was Systemic, there should be transfer of training effect while exercising with the non-trained leg non-trained leg responded as if there were no training effect what-so-ever

One Legged Training Effect

Peripheral Adaptations decreases in –NE –E –LA –VE –HR these adaptations are specific to the muscles trained

How are these peripheral responses and adaptations manifested?

Peripheral Feedback Group III and Group IV nerve fibers –respond to tension, temperature and chemical changes in muscles –increase firing actions in proportion to changes in metabolic rate example of feedback mechanism

Peripheral Control Mechanisms

Central Command higher brain centers initiate command to perform task –physiological responses are adjusted to meet expected demand (sympatheti, Q, V) if more motor units are recruited to develop tension, greater physiological adjustments are instigated to meet expected metabolic demands example of feedforward mechanism

Central Control of Motor Unit Recruitment

How are these controls related to adaptations observed after endurance training?

Prior to Training To perform a fixed sub-maximal workload motorunits must be recruited more “mitochondria poor” muscle fibers must be recruited to perform the task –greater central drive –greater peripheral disruption of physiological homeostasis (H+, adenosine, lactate)

After Training more mitochondria in muscle fibers fewer motor units needed to perform same oxidative work reduced central command reduced peripheral disruption of homeostasis (H+, adenosine, lactate)

Physiological Effects of Strength Training

Terms Muscular Strength - maximum force a muscle or group can generate (1- RM) Muscular Endurance - ability to perform repeated contractions against sub-maximal load Law of Initial Values - applies to strength training as well as endurance training and VO2max

Principles of Strength Training Overload Specificity Reversal –all apply in similar respects to endurance training low reps/hi load (2 - 8 reps) build strength hi reps/low load ( reps) build muscular endurance

Training Studies most training studies are of short duration ( weeks) in these studies, most strength gains are a result of neural adaptation –learning –coordination –ability to recruit prime movers in long-term, strength gains result of increases in size of prime movers

Neural and Muscular Contributions to Strength

Neural Adaptations in contrast to endurance training, transfer of adaptation does occur –transfer of motor unit recruitment is responsible, not hypertrophy improved synchronization of motor unit firing improved ability to recruit motor units

Muscular Enlargement Type I vs. Type II –type II produce more force than I –type II increase in size more than I –high rep/low weight results in smaller size increases than low rep/ high weight may also result in more slow twitch (muscular endurance)

Strength vs. Endurance strength training does not result in increases in capillary density (decreases due to muscle enlargement) training hi reps can alleviate this to an extent (size vs. capillaries) mitochondrial density also reduced ( size vs. mito)

Hypertrophy vs. Hyperplasia hypertrophy - increase in muscle size w/o increase in number of fibers hyperplasia - increase in number of fibers strength training results in increases in size due to hypertrophy generally believed hyperplasia does not occur in humans

Simultaneous Strength and Endurance Training. Generally…. Performing strength and endurance training simultaneously results in more favorable capillary density and mitochondrial adaptations than strength training alone

endurance training may attenuate strength gains to a certain extent strength training may enhance endurance training (ie. 80 % VO2max) monotony

Evidence 10 weeks of combined strength and endurance training resulted in –similar VO2max gains compared to endurance only –similar strength gains until week 9 when they leveled off compared to strength only

10 weeks of 3 x week strength training added to endurance program after endurance adaptations had leveled off –30 % gain in strength –no hypertrophy –~ 20 % improvement in time to exhaustion at 80% VO2max

Take Home Message endurance training can attenuate or entirely compensate for the “negative” responses to strength training without detracting from the strength gains to a great extent –capillary density –mitochondrial density

strength training may enhance endurance training by –increasing the amount of contractile protein available to perform oxidative work and.. –compensating for training monotony